1. Field of the Invention
This invention relates to an automatic white balance system.
2. Description of the Related Art
In recent years, demand for digital cameras has been growing.
The image taken by a digital camera has color tones conforming to the characteristics of the CCD or CMOS image sensor elements. To make the color tones conform to the characteristic of the human eye, various image correcting processes are carried out in the system.
In the image correcting processes, a white balance adjustment is such that, for example, red and blue are adjusted with respect to white to correct the white when an incandescent electric lamp or a fluorescent lamp is used as a light source, with white from the sun as a light source being a reference. Then, the white balance adjustment is generally made in an automatic white balance system (hereinafter, referred to as an AWB system) (for example, refer to Jpn. Pat. Appln. KOKAI Publication No. 4-304093).
In the AWB system, whether the white balance of the captured image has to be adjusted is judged at a color judgment unit on the basis of the YUV signal. The white balance adjustment is made by feeding back the white balance adjustment gain calculated on the basis of the YUV signal in the system. A color separation and synchronization unit color-separates the image signal of the captured image into a red, a green, and a blue signal and synchronizes them and, on the basis of these signals, generates the YUV signal.
When whether a white balance adjustment is needed is judged on the basis of the YUV signal generated exclusively for the color judgment unit, the color separation and synchronization unit is provided for the color judgment unit only. However, since the color separation and synchronization unit uses a line memory, the circuit size of the automatic white balance system increases considerably.
To solve this problem, a color judgment is made using the YUV signal white-balance adjusted by a feedback process without providing the color separation and synchronization unit exclusively for the color judgment unit. In this case, however, a color judgment is made on the basis of the white-balance-adjusted YUV signal influenced by the white balance adjustment gain. Accordingly, there is a possibility that a normal color judgment cannot be made, depending on photographing conditions.